The present invention relates to a magnetic recording and reproducing system in magnetic disk apparatus, video tape recorders, etc., and more particularly to a magnetic head--medium system for perpendicular magnetic recording suited to high density magnetic recording.
A conventional magnetic recording system has been such that, using a ring type magnetic head, magnetization is caused to remain in the planar direction of a magnetic recording medium so as to record a signal. With this system, however, a demagnetizing field in the medium increases with enhancement in the density of the recording, and the recording density is limited by itself. On the other hand, the perpendicular magnetic recording which utilizes a magnetization perpendicular to the plane of a magnetic recording medium has recently been proposed. This system has come into the limelight as a system wherein the demagnetizing field in the medium approaches zero with enhancement in the recording density. Regarding the perpendicular magnetic recording system, the principle has already been proposed, and excellent short wavelength characteristics, that is, the possibility of high density recording have been demonstrated.
FIG. 1 is a diagram typically showing the combination of a magnetic head 1 and a medium 2 in an example of a hitherto-known perpendicular magnetic recording system which adopts a closed magnetic path structure and which is considered the most efficient. Numeral 11 designates a first magnetic pole for recording and reproduction, numeral 12 a coil for causing a signal current to flow therethrough, and numeral 13 a second magnetic pole for forming a closed magnetic path. In addition, numeral 21 indicates a magnetic recording medium layer having perpendicular magnetic anisotropy (hereinbelow, termed "perpendicular magnetization layer"), and numeral 22 indicates a high magnetic permeability layer for forming the closed magnetic path.
Merely with such principle proposal, however, a high density recording cannot always be realized at a practicable level. In the perpendicular magnetic recording system as described above, there has not been an instructive principle which concretely teaches the magnetic characteristics and geometries of the respective magnetic poles and perpendicular magnetization layer for obtaining satisfactory results, and the respective magnetic characteristics and dimensions have been combined without a definite plan. Needless to say, a favorable result is not always obtained under such situation.
For example, the dimensions of the first magnetic pole concern the recording density characteristic, and a high recording density cannot always be realized merely by fabricating the magnetic head of the structure shown in FIG. 1. In practical use, the perpendicular magnetic recording system is also required to have recording and reproducing efficiencies nearly equal to those of the conventional recording system and to be usable up to a high frequency band. The principle proposal as shown in FIG. 1 does not satisfy the requirements fully.
The following references are cited to show the state of the art; (i) U.S. Pat. No. 3,120,001, (ii) Japanese Laid-open Patent Application No. 52-55513, and (iii) Japanese Laid-open Patent Application No. 55-8690.